1. Field of the Invention
This invention relates to corrosion inhibition and more particularly to the inhibition of the formation of white rust on galvanized steel.
2. Description of the Prior Art
Galvanized steel is extensively used in the form of flat rolled sheet and strip, rod, wire, fasteners and the like where protection against corrosion for steel articles having a light section are utilized. The steel provides the strength to the article while the zinc coating on the steel provides corrosion protection.
When used herein "galvanized steel" means steel coated with zinc by hot-dip sheet galvanizing, continuous (strip) hot-dip galvanizing, and electro-galvanizing. Galvanized steel is comprised of a steel substrate coated with zinc. The galvanized steel has three different layers, the steel, steel zinc alloys or mixtures, and zinc. In the processes for producing galvanized steel, the steel is coated with zinc and an inorganic coating, usually containing hexavalent chromium, is applied to the finished galvanized steel. Illustrative of such chromium coatings are those of the type disclosed in U.S. Pat. No. 3,620,777. The hexavalent chromium coating is used, in part, to prevent the formation of "white rust" which is the corrosion product of zinc. As used herein "white rust" is synonymous with "wet storage stain" which in the majority of instances, is white in color. However, under certain conditions, black and other colored chromium products may be encountered. Although the chromium coating provides some protection to the zinc, galvanized steel which is stored for even short periods of time develops white rust and thus becomes undesirable for the particular end use. Further, hexavalent chromium compounds have been questioned as potential health hazards and the steel industry has actively been engaged in pursuing methods of preventing white rust while eliminating the need for chromate coatings.
In accordance with the present invention, a method and composition are provided for the inhibition of white rust.